This invention relates generally to well drilling or completion operations, and to the attachment of downhole isolation, production, or testing tools to casing or other work strings. In particular, the invention is directed to the attachment of isolation tools, such as an inflatable casing packer, or other production or testing tools, in a manner that reduces or eliminates welded connections.
In the oilfield industry, isolation, production, or testing tools are often attached to casing or other work strings in order to run the tool downhole into the wellbore. A casing string, or work string, is generally made up of a series of jointed steel pipe or tubing. The string is run into the wellbore with tools attached to perform one or more specific functions. The current invention relates primarily to the use of a tool known as a packer.
A packer is used to plug an area in a well by sealing off the annulus between the string on which the packer is run and the next outer casing (or the wellbore itself). Packers are well known in the art. One particular type of packer is an inflatable packer. Inflatable packers are run on the casing string, and inflated when the desired position in the well is reached, sealing the annulus at that particular location. Such inflatable packers, also called annulus casing packers, have a number of uses in well operations, including isolating producing zones, preventing gas migration, supporting or squeezing cement, or isolating liner hangers.
In general, inflatable casing annulus packers are made up of a casing mandrel, an inflatable element, and an inflation mechanism. The prior art annulus casing packers were commonly constructed such that the body of the tool was welded to the casing mandrel. Often multiple welds were employed, welding the casing to a sleeve disposed between the inflation mechanism and the coupling at the end of the tool, and welding the sleeve to the inflation mechanism. These welds add time and expense to the development of the tool. More importantly, welding can affect the metallurgy of the casing, making the welded area subject to attack, for example by corrosive well fluids. As such, welding to the casing or to coupling is at minimum undesirable, and may be prohibited under certain industry standard regulations.
Alternatively to the welded connection, it has been attempted to connect the inflation mechanism to the casing mandrel using adhesive or epoxy. However, the extreme conditions to which the tool is subject when run downhole into the portion of the wellbore that is of interest can include several thousand psi of pressure and/or temperatures over several hundred degrees Fahrenheit. Such conditions can have a detrimental effect on adhesion, potentially resulting in a failure of tool. As such, mechanical connections are preferable.
The ability to mechanically thread the casing mandrel to the inflation mechanism is limited by the need to maintain a minimum acceptable wall thickness, and inside diameter, in the casing mandrel. In general, for a five-inch nominal diameter casing the depth of a thread or groove in the casing mandrel should be no more than xc2xd of one percent of the inside diameter. This makes it difficult to create a threaded connection that is sufficient to resist the various tensile, compressive, and shear forces imposed on the fully loaded tool.
The disadvantages of welded, adhesive, and threaded connections in the coupling of the inflation assembly to the casing mandrel in an inflatable annulus casing packer to the casing mandrel are overcome by the present invention.
In addition, although the connection of the present invention is described with regard to its use with an inflatable packer, the invention is applicable to various other oilfield tools that are connected to casing or work strings for use in drilling, completion, production, or workover operations.
It is an aspect of the current invention that a tool, such as the inflatable annulus casing packer described in detail below or other isolation, production, or testing tool, may be attached to a mandrel in a manner that is highly resistant to axial movement. It is a further aspect of the invention that the mechanical connection is made using non-adhesive components combined in such a manner that they will resist the high temperatures, high pressures, and corrosive fluids and gases that may be encountered in the well.
In the embodiment described herein, the system of the present invention provides a high-strength non-welded mechanical connection between a casing mandrel and a valve assembly used to regulate hydraulic pressure and thereby inflate the inflatable element of a casing annulus packer. In general, the connection system includes at least one groove or channel cut in an outer wall of the casing mandrel. In preferred embodiments, the groove or channel is sufficiently shallow to avoid significantly thinning the wall thickness of the casing, and thereby ensures that compliance with industry standards is maintained.
The inside surface of the valve assembly, or other inflation mechanism, contains at least one partially or fully annular slot oriented to correspond with the groove(s) in the outer wall of the casing mandrel.
At least one lock is situated in the corresponding slot and the groove. The lock engages the flanks of the slot and groove sufficiently to resist shears loads applied by compression or tension in the string, and thereby restrains axial movement of the valve assembly relative to the casing mandrel. In a preferred embodiment, the lock is one or more wires, although other mechanical locking devices may be installed to provide the same function.
In a preferred embodiment, the system includes annular grooves in both the inner casing mandrel and the inflation mechanism or other tool. When multiple grooves are employed the grooves may be spaced apart, and a plurality of wires fed into the channels created by the corresponding pairs of grooves. In other embodiments there may be a single pair of aligned helical grooves, and a single wire or other lock installed.
In an embodiment of the invention, the wire or lock has relatively greater yield strength than the tool or the mandrel. As such, if the bearing surfaces of the connection begin to fail under shear, the yielded metal of the tool or the mandrel will be pushed axially, eventually bunching up and jamming the mechanism from further axial movement. As such, the current invention also provides a failure mode in which the inflation mechanism is rigidly fixed by the yielded metal, sealing the packer in its position and preventing failure of the inflatable portion.
It is another aspect of the current invention that the time to manufacture the tool, and the expenses involved, may be reduced by the novel form of attachment. In addition, welding between the valve element and the casing is eliminated, which reduces changes to the metallurgy of the tool, the invention reduces the number of areas particularly vulnerable to corrosive attack.